This invention relates to railroad crossties, more particularly, to laminated wooden railroad crossties.
In the conventional construction of railroad wooden crossties, a tie plate carrying a rail is disposed upon the surface of the wooden tie. As a train passes over a crosstie, a load is imparted to the crosstie through the rail and tie plate. The tie plate spreads and distributes the load to the crosstie surface beneath the tie plate. The area of the tie beneath the tie plate is commonly referred to as the wear area because this is the area that tends to disintegrate sooner than do the other areas of the tie.
Conventionally, spikes are driven through holes that are disposed near the lateral edge of the tie plate and lodged in the crosstie. These spikes secure the rail to the tie plate and likewise secure the tie plate to the wooden tie to restrict horizontal and vertical movement of the rail as a train passes over the rails.
Customarily, each of the two rails of a railroad track are canted inwardly by the tie plate being disposed at a slope of one unit of rise to forty units of run, to improve the load bearing qualities and to help maintain the gauge (distance between the rails) of the rails, particularly when a train passes. Actually, the spikes primarily hold the gauge. Because each rail is canted inwardly of the track, the passing of train wheels over the track tends to cause slight amount of horizontal movement to occur in conjunction with a slight amount of vertical movement of the rail. This combination of vertical and horizontal motion tends to effect a rocking movement of the tie plate and tie, which movement in turn causes an indentation in the tie; a phenomena known in the railroad industry as tie or plate cutting, i.e., the cutting or wearing of the wooden tie in the tie wear area. This plate cutting is accelerated by a number of factors. For instance, moisture under the tie plate softens the wood fibers of the wear area. Dust and abrasive particles from the road bed become trapped under the tie plate; consequently, the rocking movement of the plate under the load and vibration of passing trains literally grinds the abrasive particles under the tie plate into the tie, destroying the supporting characteristics of the wood fibers of the tie in the wear area. Because of this wearing or plate cutting, ties must be replaced often.
Hardwoods such as red and white oaks, tupelo, sweetgum, and beech have been the most popular type of wood for employment in construction of railroad ties because of hardwood's superior wear characteristics. However, one particularly favored type of hardwood used to construct crossties is oak. However, the available supply of hardwood fluctuates. Unexpected forest fires and droughts can deplete available supplies of hardwood and supplies of hardwood are not easily replenished due to the extended growth cycle of hardwood. In addition, hardwood is increasingly being diverted to other product areas. Parenthetically, it should be noted that the construction of conventional crossties results in a high percentage of wasted wood.
Laminated wooden crossties have been proposed to allow more efficient utilization of available supplies of wood. Laminated crossties are created by laminating individual lamina to form a crosstie. The conventional laminated crosstie is constructed such that each lamina is a unitary wooden element laminated to have generally their grains parallel to one another. The lamina are bonded together, and usually chemically treated to arrest decay and insect attack.
The laminated wooden crosstie has exhibited field performance comparable to conventional unitary crossties. However, laminated wooden crossties have a purchase price much higher than that of conventional crossties. Attempts to lessen the financial impact of laminated ties has centered on improvement in the load capacity and wear characteristics of laminated ties. Improved crosstie load capability enables one to deploy fewer crossties, and improved wear characteristics results in a longer crosstie useful life. Efforts to increase the load and wear characteristics of laminated crossties have involved such suggestions as impregnating the crosstie with a plastic resin and using wooden inserts beneath the tie plate implanted in the crosstie. These suggestions to increase the load and wear characteristic of laminated crossties has met with limited success.
The present invention offers more efficient utilization of wood material. The present invention also offers superior wear resistance and load bearing capacity for crossties. The invention allows one to deploy less expensive and more plentiful softwood without appreciable degradation of crosstie performance. The invention further allows one to design a crosstie which best compliments the type of rail traffic expected to be encountered, e.g., lightweight intracity commuter rails can employ ties with a minimum of hardwood, resulting in less material costs and still derive the performance advantages of the present invention.